BLUE BELL, Pa. — President Barack Obama and potential presidential candidate Chris Christie were scheduled to drop in on Pennsylvania on Sunday to try to influence the gubernatorial campaign in the race's waning days and motivate voters in what is a relatively sleepy midterm election in the state.

Democrat Tom Wolf, a first-time candidate who ran his family business for nearly three decades, is trying to knock off Republican Gov. Tom Corbett, a conservative former state and federal prosecutor who is seeking a second term after stumbling through his first four years. In particular, Corbett has struggled to explain budget-balancing cuts in aid to public schools in 2011 at the same time he cut business taxes.

Wolf has led steadily in polls, although Corbett's campaign appears to be making up ground by warning voters that Wolf is secretly planning a massive middle-class tax increase. Wolf has said he intends no such thing and plans to restructure the state income tax rate to shift a bigger burden to higher earners. Meanwhile, with news of Obama's visit, Corbett's campaign has added a second prong to its attack, telling voters in a new TV ad that Wolf will advance Obama's agenda.

The ad tries to capitalize on Obama's sagging popularity — two recent independent polls show that just one in three voters surveyed say he's doing a good job — and it quotes first lady Michelle Obama during her Oct. 15 visit to a Philadelphia rally for Wolf: "If we truly want to finish what we started, then we need to elect Tom Wolf as governor of Pennsylvania."

Obama planned to appear on Temple University's campus with Wolf in the evening. Meanwhile, Corbett visited churches in Lancaster County in the morning and is dropping by campaign offices and diners in Philadelphia's suburbs before he meets up in Ivyland on Sunday night with Christie, the New Jersey governor and head of the Republican Governors Association.

At a campaign stop in Blue Bell, a few miles outside Philadelphia, Corbett went into a crowded campaign office to shake hands with volunteers there making phone calls to lists of registered voters.

Pollsters are projecting turnout to be lower than in past midterm elections; turnout was slightly above 50 percent of registered voters in 2006 and about 47 percent in 2010.

Christie has been to Pennsylvania to campaign or fundraise with Corbett at least four times in the last few months. In Philadelphia, Obama will try to motivate the city's huge Democratic voting base that tends to have less impact in midterm elections. In 2010, just 40 percent of registered Philadelphians cast a ballot.

Corbett is deeply unpopular in Philadelphia, whether because of his first budget that delivered a heavy blow to the city's financially troubled schools or his signature on a tough voter identification bill that ultimately was struck down in court.

To a large degree, the gubernatorial election will be won or lost in Philadelphia and its four suburban counties: Bucks, Chester, Delaware and Montgomery. Pennsylvania has nearly 8.3 million registered voters, and one in three lives in Philadelphia or its suburban counties.

A high voter turnout in Philadelphia, the state's largest city, would favor Wolf, with Democrats making up almost 80 percent of the city's 1 million-plus registered voters.

In addition, the candidate who wins Philadelphia's four suburban counties, a crucial swing area of 1.6 million voters, is nearly assured of a victory. Beginning with the 2000 election, all but one candidate for U.S. Senate, governor and president who has won Pennsylvania also carried Bucks, Chester, Delaware and Montgomery counties. The exception was Republican U.S. Sen. Pat Toomey in 2010.